Generally, photodiodes are semiconductor diodes that are used to convert photons into an electrical current. For example, a photodiode may be used to convert an optical signal into an electronic signal in an opto-electronic circuit, or placed at any location in which incident light detection is desired.
Presently, one type of manufactured photodiode—so called MSM for metal-semiconductor-metal—includes a portion of quality semiconductor material sandwiched in between two metallic plates and a voltage is applied to the plates. When incident light in a broad range of wavelength reaches the semiconductor material, a plurality of electron-hole pairs are created. The electrons will travel in one direction, e.g., toward the positive plate, and the holes will travel in the opposite direction. The incident light is then detected by monitoring the current running though the photodiode circuit.
However, there are pluralities of problems with the present state of photodiodes. One of the problems is the expense of manufacturing the photodiode. That is, in order to provide the best level of detection, present photodiodes require extremely high quality semiconductor material such as single crystal silicon. For example, in order to detect the most minimal of electron-hole pairs, the semiconductor material crystal structure must be as flawless as possible to ensure a minimum of interruptions in the travel of the electro-hole pairs. Thus, the present manufacturing method realizes a great expense in both material and quality control.
Another problem with the present state of photodiodes is the amount of semiconductor material needed to form the photodiodes. For example, when detecting light, the best of the photodiodes utilizes semiconductor material between the metal plates having a width of approximately the wavelength of the light being detected. Therefore, not only is the semiconductor material very expensive in material and quality control, but a large quantity of the high quality semiconductor material is required for the photodiode.
Yet another problem with the present state of photodiodes is the speed of the diode. For example, the electric field of a photodiode is defined by the voltage applied divided by the distance between the electrodes. As such, turning on, e.g., windowing, the photodiode can take an amount of time due to the need to ramp up the voltage to the required level to make the photodiode operational. This ramp up time takes time which results in a delay between the turning on of the photodiode and the actual operation of the photodiode. Moreover, because of the width of the semiconductor material, the drift, e.g., the time it takes an electron-hole pair to cover the width of the silicon and reach the plates, also provides a delay in the overall photodiode detection speed. If the speed wants to be increased, one needs to apply more voltage to the photodiode, producing more dark current.